Research performed over the last few years identified nitric oxide (NO) as an intracellular signaling molecule involved in regulation of plant physiological processes at all stages of the life cycle. Nevertheless, some extremely important aspects of NO biology are still far from being clarified. There exist different points of view on NO formation and utilization in plants. The mechanisms of perception and transduction of the NO signal are not yet fully understood, and the origin of specificity underlying coordinated activation of responses to NO remains unresolved. It is reasonable to expect that the deep knowledge of NO functioning in animals may provide some keys to these questions. Such a comparative analysis is a way to reveal similarities and emphasize the differences in the current understanding of the NO role in plants. The present lecture highlights these aspects of NO functioning.